LED packages have been developed that include an LED die and a submount that includes a diode, such as an ESD diode. However, current LED packages require manufacturers to develop and implement many separate electronic components in order to power the LED dies and to control the light coming from the LED dies. A need exists to simplify the challenges of powering and controlling LED packages.
Power supplies used in LED lighting systems have often been based on power supplies for conventional lighting systems or other electronic devices, leading to problems of inefficiency, lack of reliability and lack of longevity. Accordingly, a need exists for power supplies designed and optimized for LED lighting systems.
Incandescent lighting sources are a simple resistive load to the power network. Over the years, the increased acceptance and use of fluorescent and HID lamps has increased the use of electronics to drive loads and these devices, along with computers and appliances, have introduced some side effects due to the ballasts and power supplies they incorporate. The electrical current these newer systems draw is very different from resistive loads and introduces issues for electricity consumers and providers. These issues arise from the power supplies. Switching power supplies are small and efficient compared to the linear supplies used in the past. However, they introduce distortions of the input current. Switching supplies draw current in pulses and not in a smooth sinusoidal fashion. Thus the alternating voltage (typically a 50 or 60Hz sine wave in most power distribution systems) and current are often out of phase. This distortion causes problems with power distribution with the local grid and can introduce capacity issues in power distribution and local circuits.
For a simple resistive load the power factor is unity or 1.0. For switching supplies however the power factor can be as low as 0.6. Fixing low power factor is accomplished through the use of power factor correction (PFC). Good quality PFC can bring that ratio to 0.99 thus mitigating the problems associated with poor power factor.
Since LEDs and most electronics are low voltage systems, the use of power conversion is quite common. In many cases, there is an off-board power supply that is plugged into the wall and provides lower voltage AC or, more typically, DC power. Thus high voltage and low voltage systems are often separate. In most consumer electronics these power supply systems are integral to the device; that is, they plug directly into the wall. This is most practical for most electronics and eliminates the need for separate boxes for power supplies and electronics.
In most current LED systems, the off-board supply is used because it can supply energy to a multitude of fixtures and keep the system cost down. The integration of such power supplies into fixtures would have been prohibitive both in cost and physical space required as well as creating a thermal issue. However, in installations where the fixtures are located apart, the additional costs of cabling in addition to maintenance issues can outweigh the initial benefits of a distributed power system.
In general the impedance of the power grid tends to be low so that delivery of power is efficient. The impedance of the power supply, or any device that uses power, should not be non-linear otherwise it can generate harmonics on the power line and this is wasteful and undesirable. This also reduces power factor. A need exists for methods and systems for improving power factor for LED lighting systems.